INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2020

The following table reconciles the federal statutory tax rate to the effective income tax rate from continuing operations:

	2020				2019				2018
Tax at statutory rate		21.0		%		21.0		%		21.0		%
State income tax, net of federal benefit		6.9				12.2				(1.4	)
Federal and state tax credits		5.3				4.0				3.9
Stock-based compensation		(0.5	)			(0.8	)			2.1
Net operating loss not benefitted		(6.9	)			(5.8	)			(4.3	)
Other		(0.3	)			(0.2	)			(5.5	)
Change in valuation allowance		(25.5	)			(30.4	)			(15.8	)
Effective tax rate		0.0		%		0.0		%		0.0		%

. Significant components of our deferred tax assets are as follows:

	December 31,
	2020			2019
	(In thousands)
Net operating loss carryforwards	$	217,100		$	204,600
Federal and state tax credits		42,800			38,400
Capitalized research and development		6,000			5,900
Stock-based compensation		9,400			7,700
Operating lease liabilities		1,200			700
Other		2,100			1,200
Total deferred tax assets		278,600			258,500
Less: valuation allowance		(277,200	)		(257,900	)
Net deferred tax assets		1,400			600

Operating leases, right-of-use assets		(1,400	)		(600	)
Total deferred tax liabilities		(1,400	)		(600	)
Total net deferred tax assets	$	—		$	—

A reconciliation of the beginning and ending amounts of unrecognized tax benefits is as follows (in thousands):

Balance as of December 31, 2019	$	17,700
Decrease related to prior year tax positions		—
Increase related to current year tax positions		1,400
Balance as of December 31, 2020	$	19,100